Field of the Invention
The invention relates to an exposure mask having a substrate to which a phase mask, which at least partially attenuates radiation, is applied. A phase-shifting dummy structure, which influences the optical properties of the radiation but is not visible in an exposed image, is applied to the substrate. The dummy structure has a defect and a repair structure for the defect in the dummy structure is applied to the substrate. The repair structure has a greater width than the dummy structure. Exposure masks are used, for example, in semiconductor technology to produce etch structures. For exposure of small structures, it is necessary to use phase masks as exposure masks in order to achieve a high resolution of the structures which are to be exposed. Phase masks have a phase-shifting property and, moreover, a low transmission. The phase shift of the radiation passing through the phase mask results in more precise imaging of the phase mask on a substrate that is to be exposed, such as for example a photoresist.
Furthermore, it has been found that arranging phase-shifting dummy structures on the exposure mask further improves the resolution of the structures which are to be exposed. A phase-shifting dummy structure leads to the electromagnetic field of the radiation being influenced in such a manner that the structure which is to be imaged can be imaged accurately without the dummy structure itself appearing during an exposure operation. The use of dummy structuresxe2x80x94referred to as anti-scattering bars (ASBs)xe2x80x94is described, for example, in international PCT publication WO 99/47981 and U.S. Pat. No. 6,312,854 B1.
During the fabrication of very small structures, which are required, for example, for the fabrication of semiconductor components, in particular semiconductor memory components, the dummy structures are very narrow at least in terms of width. Therefore, the dummy structures are fabricated from a material which can be applied at low cost to exposure masks in the required geometries. In this case, by way of example, a molybdenum silicide layer is used, which has a low transmission in the region of 6% and effects a phase shift with respect to the substrate material, which preferably consists of glass, of 110 to 180xc2x0 C. If defects, such as for example interrupted dummy structures, occur during fabrication of the dummy structure, these defects are repaired using a repair layer. In previous repair methods, repair structures which have substantially the same optical properties as the dummy structure have been applied.
It is accordingly an object of the invention to provide an exposure mask with a repaired blind structure and a method for repairing an exposure mask, which overcome the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which leads to an exposure mask with improved optical property.
With the foregoing and other objects in view there is provided, in accordance with the invention, an exposure exposure mask formed on a substrate, the mask comprising:
a phase mask for at least partially attenuating radiation;
a phase-shifting dummy structure formed to influence an optical property of the radiation but to be substantially invisible in an exposed image, said dummy structure having a defect; and
a repair structure for repairing the defect in said dummy structure, said repair structure having a greater width than said dummy structure and having a lower phase shift than said dummy structure with respect to a material of the substrate.
A significant advantage of the novel exposure mask is that the repair structure has a lower phase shift than the dummy structure with respect to the substrate material. Tests have shown that, on account of the broader geometry of the repair structure, it is advantageous to use a repair structure with a lower phase shift with respect to the substrate material than the phase shift which is produced by the dummy structure. In this way, a greater optical quality of the exposure mask can be achieved.
With the above and other objects in view there is also provided, in accordance with the invention, a method of repairing an exposure mask on a substrate, the mask having a phase mask on the substrate, for at least partially attenuating radiation and generating an exposure structure during exposure. The method comprises the following method steps:
forming a phase-shifting dummy structure on the substrate, for influencing optical properties of the radiation but not producing an exposure structure upon an exposure, the dummy structure having a defect;
forming a repair structure on the substrate, for repairing the defect, the repair structure having a greater width than the defect, and the repair structure is produced from a material having a lower phase shift than the dummy structure with respect to the substrate material.
In accordance with an added feature of the invention, the repair structure has a lower transmissivity than the dummy structure. Forming the repair structure from a material which has a lower transmission coefficient than the dummy structure results in an improved optical property of the exposure mask during exposure.
A particularly simple and inexpensive embodiment of the exposure mask is achieved by the fact that a repair structure which allows substantially no transmission is used, i.e., when the repair structure is substantially opaque. This minimizes the phase shift of the repair structure in a simple manner.
The repair structure preferably does not have any phase shift with respect to the substrate material. This allows optimum formation of the repair structure.
In accordance with an additional feature of the invention, which provides for a simple and inexpensive embodiment of the repair structure, the material of the structure is at least partly composed of carbon. It is preferable for the repair structure to consist only of a carbon compound. The use of carbon offers a simple and inexpensive method for producing the repair structure with the required small feature size.
In a simple embodiment, the repair structure is oriented substantially in accordance with the dummy structure and arranged symmetrically above the defect with respect to a longitudinal axis of the dummy structure.
Tests have shown that, depending on the structure of the dummy structures, a laterally offset arrangement of the repair structure with respect to the defect but at substantially the same height as the defect results in an exposure mask with improved optical properties.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in an exposure mask with repaired dummy structure, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.